Worse by degrees

Aug. 14, 2008

Highway planners are being warned by some very recent in-depth studies and notable weather-induced events in the past few years that roads, bridges and tunnels will be increasingly subjected to severe, sometimes rapid climate change that can cause significant damage to that transportation infrastructure.

Highway planners are being warned by some very recent in-depth studies and notable weather-induced events in the past few years that roads, bridges and tunnels will be increasingly subjected to severe, sometimes rapid climate change that can cause significant damage to that transportation infrastructure.

Many state and other transportation officials are starting to take those warnings seriously—thinking about, planning or even developing structures that are designed to protect against such dire consequences, or at least to cope with them should they occur. But many others are doing very little as yet, because they have just been learning about the expected problem, are not yet convinced it is going to affect them much or cannot afford to plow money into what they regard as a really long-range project, as they focus much more attention on trying to moderate climate change by controlling vehicle emissions.

“You’re just now hearing the term ‘climate change’ and its impacts. A year ago I don’t think we’d be having this discussion,” said Malcolm Kerley, chief engineer for the Virginia Department of Transportation. But there is no doubt, said Thomas Peterson, a research meteorologist at the National Oceanic and Atmospheric Administration (NOAA), that “the climate is changing, and it’s going to be changing rapidly in the future.” And referring to the most prominent threat, Peterson said, “It isn’t just a question of storm surge, but storm surge on top of sea-level rise.”

The kinds of more frequent and more severe events that are expected to be caused by global warming are, especially, greater rises in sea levels, accentuated by stronger storm surges; hotter and more intense heat waves; heavier precipitation; more robust hurricanes; and, in Alaska, more melting permafrost below highways. Already, in recent years, transportation structures have been damaged or even washed away by such climate-wrought events.

In Texas, for example, “we have started evaluating our bridges along the coastline, to see if they will be able to withstand storm surges,” said John Barton, assistant executive director for engineering operations at the Texas Department of Transportation (TxDOT). “We want to make sure that we don’t have the experiences” that Louisiana, in particular, suffered because of Hurricane Katrina in 2005. Historically, Texas transportation planners have designed bridges to withstand what they expect will be the most severe climate over the next 50 years, but “all the climatologists tell us these events will be more frequent,” Barton said.

“Our history is not a good predictor now, with all this climate change,” he added. In late 2006 and early 2007, the El Paso area, mostly desert with typical annual rainfall of 6 to 9 in., had 10 in. of rain in one day and 30 in. over several days, he recalled. “Those types of events are occurring all over the state. As we repair roads or build new ones, we have to take into account that these events are occurring more frequently,” and with more severity.

With the cost squeeze that plagues states, it is a balancing act. “You don’t want to build something, just to have it destroyed in a storm, but you don’t want to build it so strong that it’s more than needed,” Barton said.

Other weather-induced disasters that have caught planners’ attention include hurricanes Katrina and Rita, along the Gulf Coast in 2005; the second major Mississippi River flooding in the Midwest in 15 years, in June of this year; and rampant wildfires in California and Florida in recent months.

Major blows

Now, several studies by impressive committees of climatologists, transportation planners or builders, economists, consultants and others predict that things can—and almost certainly will—only get worse in the years to come, whatever success nations may have in reducing greenhouse gases that help fuel global warming.

One of these studies, titled “Special Report 290: Potential Impacts of Climate Change on U.S. Transportation,” concluded that potentially the greatest impact of climate change on North America’s transportation system will be flooding of coastal roads, railways, transit systems and airport runways, “because of a global rise in sea level coupled with storm surge and exacerbated in some locations by land subsidence.” But vulnerability “will extend well beyond coastal areas,” said the report, assembled by a committee of experts under the auspices of the Transportation Research Board (TRB) and the National Research Council’s (NRC) Division on Earth and Life Studies.

The panel said some 60,000 miles of coastal roads alone already encounter flooding and called on policymakers to inventory vulnerable infrastructure with a view to planning how to protect or reinforce them, or else replace them or move them to higher ground. Climate change should be incorporated into their long-term capital improvement plans, facility designs, maintenance, operations and emergency response plans, the committee said.

“The main thing we’re trying to do with this report is say that this is an issue they’ll have to deal with regardless of any reduction in greenhouse gases,” said George Eads, an economist at CRA International and a member of the TRB-NRC committee that did the study. The report also emphasized a need for climatologists and transportation officials to communicate with each other better—for climatologists to provide location-specific predictions of how climate change is likely to affect roads, bridges and tunnels, among other structures. Robert Gallamore, another panel member who heads the Gallamore Group, a transportation consulting firm in Rehoboth Beach, Del., referring to so-called 100-year events (storms so severe that they are expected to occur only once a century), said, “There are going to be many such events in a hundred years,” due to global warming.

The report has a raft of recommendations for preventing or coping with infrastructure damage from climate change, including developing new heat-resistant materials; elevating and protecting streets and bridges to meet storm surges; adding drainage canals near coastal roads and more pumping capacity for tunnels; protecting bridge piers and abutments from heavy precipitation with riprap; tying bridge decks more securely to substructures; strengthening foundations; and using modular construction where infrastructure may fail.

This and other studies have gained considerable attention, “and transportation people are starting to take notice,” said Henry G. Schwartz Jr., the TRB-NRC panel chairman, who is retired chairman and president of Sverdrup/Jacobs Civil Inc., an engineering firm. DOTs, metropolitan planning organizations and other groups are taking inventory of infrastructure that will be vulnerable with an eye toward factoring this information into their overall planning, he said.

“It’s not as if we’re going to run out and lift all coastal bridges seven feet,” but when rebuilding, ultimately, it is going to be a cost-benefit issue, Schwartz said. North Carolina DOT officials are aware that if they replace the Herbert C. Bonner bridge, they need to accommodate rising ocean levels over the next century so the new bridge does not become engulfed by storm surges, he noted.

Design standards have to be based on probabilities, not on the certainty that planners have wanted in the past, the committee chairman said. “If you wait 100 years to become certain, it’ll be too late.” He said, “Things have changed in the last 30 years. The slope of the curve has changed.” In the Midwest, for example, “Inside of 15 years, we’ve had two 100- to 500-year (flood) events.”

Can’t just coast

A longer study by the U.S. Department of Transportation’s Federal Highway Administration (FHWA), aided by Cambridge Systematics and the U.S. Geological Survey, among others, looked at 2,400 miles of roads, for instance, that were underwater from climate-produced events along the Gulf Coast, between Mobile, Ala., and Galveston, Texas. It postulated what would happen with sea rises of 2 or 4 ft. More than half of the area’s major highways (64% of interstates and 57% of arterials) are below 23 ft in elevation “and subject to flooding and possible damage due to hurricane storm surge,” the report said.

Michael Savonis of the FHWA, who helped prepare the study, noted some of its conclusions in a recent American Meteorological briefing: Average Gulf Coast temperatures are likely to increase by 2 to 4°F, the number of days over 90° by 50%; rainfalls will be more intense; impacts will worsen as emissions increase; and, he said, “Current practice focusing on a 20-year time frame is not well-suited to the assessment of impacts due to the natural environment.”

The study, “The Impacts of Climate Change and Variability on Transportation Systems and Infrastructure: Gulf Coast Study, Phase I,” is to be followed by other phases that take a closer look at areas along the Gulf Coast and delve into detail as to how transportation officials can adapt to climate change. The study region has 17,000 miles of major highways and is home to the largest concentration of freight-handling ports in the U.S.

Other studies have been done or are in the works, but many of them concentrate on preventing global warming and deal little, if at all, with its impact on the transportation infrastructure. One analysis is being done as part of a series for the Environmental Protection Agency, by NOAA, the U.S. Geological Survey and the federal DOT, and is titled “Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region.” It warns that one impact of sea-level rise will be a decrease in clearance for vessels under bridges; those connecting coastal barriers and spans that contact the mainland to islands and spend their lives in salty water will find more of their support structure immersed or their decks closer to water, with increased maintenance problems. Also, highways and causeways will flood sooner.

While climate change will have “a significant impact on bridges and all infrastructure, the planning is just beginning to come into view,” said Ken Kobetsky, program director for engineering at the American Association of State Highway & Transportation Officials (AASHTO). Among state DOTs, “I think there’s an initial awareness, but it varies” by state, Kobetsky said.

The Pew Center on Global Climate Change said that as of last January, 11 states had started adaptation planning efforts or adopted adaptation strategies. Some city/county groups are including impact on infrastructure in their climate-change probes, including New York City, King County, Wash. (Seattle) and Miami-Dade County in Florida.

Many DOTs and other agencies are doing very little about the problem, partly because they say they need locale-specific predictions of the impact of climate change; more global forecasts do not help, they say. “We haven’t seen any science that would warrant going beyond what we are doing now,” said Charles Carrier, a spokesman for the New York State DOT. “It would take resources that are very tight,” and the agency faces a budget cut as it spends “a lot of money to keep everything in good state of repair.”

“Infrastructure is at risk unless local community and state officials change their planning,” said Doug Hecox, an FHWA spokesman. “There’s a real price being paid for doing nothing.” But some states are moving, or at least considering either anticipating climate change or responding to climate-induced damage that their infrastructure has already sustained.

Making adjustments

“This has been a hot topic,” said Luise Paiewonsky, the Massachusetts state highway commissioner and a member of the TRB-NRC study committee. “The fact is, climate change is upon us now—we can’t just try to prevent it.” Her agency has begun an inventory of vulnerable infrastructure and may have to adjust the construction season and crews’ working hours to adapt to global warming’s effects, change pavement mixes to withstand extreme heat and expand protection for bridges (learning from the way Katrina lifted bridge decks off the piers), she said.

“We may need to look at design standards at their core, to make sure designs take into account the impacts of climate change,” Paiewonsky said. “We’re not saying that states have to start from scratch,” but “it’s important not only to develop and improve our strategies, but to share our best practices with one another,” for considering climate change when new projects or revamped ones are planned. She said, “In some cases, we’ll be taking entirely new approaches, and in other cases, modifying” practices. “It’s time for people to sit up and take notice. Climate change poses a real challenge to transportation planners, but it also taps into some of the things they do best.”

“We know what’s going to be worse—we just don’t know how much worse, or when,” said Raja Veeramachaneni, director of planning and preliminary engineering for the Maryland Highway Administration. Bridges need to be protected from scour and highways from higher flood elevations—either raised or moved farther inland; new flood-relief structures and paving materials (to permit water to seep through with less runoff) will be necessary, he said.

Like other states, California wants more specifics. Planners have to work with “micro-climate” data to show, for example, how climate change will affect the San Francisco Bay, said Reza Navai, the state DOT’s program manager for climate action. “We are already examining some of these,” he said, using some of the methods adopted to protect structures from earthquakes, but he said it is too early to know what the solution is. It could include redesign or reinforcement of structures, new materials, more use of levees and other barriers, a deeper paving sub-base and new heat-resistant asphalt and concrete. “We routinely include natural climate changes” and their effects on infrastructure, “but we understand that climate change may push these measures to the limits and beyond,” Navai said.

TxDOT is already taking steps to guard its new and existing bridges against scour caused by severe wave action, and from being washed away in a storm. Jetties, or geotubes—plastic-coated fiberglass covers filled with sand or gravel placed perpendicular to the shoreline, are used to protect bridge decks from being washed or floated away. Larger stones—24 to 36 in. vs. 18 to 24 in. previously—are used to armor the soil at the end of the bridge to prevent the soil from washing away from the bridge foundation. “The smaller stones become more buoyant quicker,” said the agency’s Barton.

Meanwhile, a stretch of I-87 that washed away in Hurricane Jerry in 1987 and has not been rebuilt (to avoid the same fate) may be moved farther inland. “Moving the road inward becomes more and more of an option,” Barton said. Also, partly because of more extreme heat’s deforming effect on asphalt and concrete, “our pavements are getting thicker,” he said. While an 8-in. base and 3-in. surface pavement used to be standard, the base is now 12 in. thick, with a 4-in. sub-base and a 2-in. surface.

Climate changes also have forced the agency to use chemicals to improve the quality of the asphalt, making it more resistant to heat as well as more elastic when it is cold. “We are starting to use more porous materials for our pavements,” using technology developed in Europe and brought first to Georgia in the U.S., which “has kind of migrated across the southern United States,” Barton said. With more rain, the water is allowed to seep through the pavement into the soil, reducing accidents caused by water on the road’s surface.

Higher level After bridges over the Bay of St. Louis and Biloxi Bay, in Mississippi, less than 20 ft above the water level, were damaged by Katrina, the state DOT had them respectively rebuilt 28 and 34 ft above that level, said Harry Lee James, the agency’s deputy director and chief engineer.

Katrina also slammed into the I-10 twin-span bridge crossing the mouth of Lake Ponchartrain, east of New Orleans, with enough force to shear off the bolts holding the roadway to supporting piers (along with gravity), dropping huge slabs of roadway into the water. The replacement bridge is being built 30 ft high, more than triple the 9-ft height of the old bridge, and the roadway is bonded to the piers with concrete. The Louisiana DOT construction builds on the experience of Florida DOT engineers, who rebuilt the same kind of bridge over Escambia Bay near Pensacola after Hurricane Ivan damaged the bridge in 2004.

Also, while the bridge was not damaged by hurricanes, the roadway leading to a bridge carrying Louisiana State Highway 1 over a vast marshland “is falling victim to coastal erosion and ground subsidence, and the existing La. 1 is literally sinking,” said spokesman Dustin Annison. Tropical storms regularly threaten the road, which often floods in low-level storms, stranding residents, tourists and the oil industry, he said. A new high-level bridge and elevated roadway at a new location will replace the old alignment, reflecting DOT concerns about storm surges.

The Virginia DOT is looking at whether to change its standards for bridge heights and protect tunnels, especially due to expected sea-level rise in the Hampton Roads area. Tying down bridge spans to counteract buoyancy caused by trapped air in a storm is being studied, as is “heavy permeable” pavement to let water seep down from the surface, said Kendal Walus, the state’s structure and bridge engineer. The agency will also look to guidelines for bridge protection now being developed by an AASHTO committee.

About The Author: Karr is a freelance writer with an office in Bethesda, Md.

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